Contour follower

ABSTRACT

A contour follower includes a plurality of sensors spaced around a waterjet nozzle, each of the sensors being configured to measure a distance between a working surface and a first plane, perpendicular to a longitudinal axis of the nozzle. The sensors may include hall-effect sensors lying in the first plane and magnets lying in a second plane, parallel to the working surface. A detecting circuit processes signals from the sensors to determine an angle of the working surface, relative to the first plane, and a distance between an aperture of the nozzle and the working surface. A collision detection sensor provides a signal in the event the device approaches to within a selected distance of an obstruction in the plane of the working surface. A shield plate blocks and dampens secondary spray-back of cutting fluid occurring at low angles above the working surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is related, generally, to waterjet cutting systems, and,in particular, to a method and apparatus for controlling the orientationand position of a waterjet cutting head with respect to a surface.

2. Description of the Related Art

Waterjet and abrasive-jet cutting systems are used for cutting a widevariety of materials, including stone, glass, ceramics, and variousmetals, including stainless steel. Such systems are capable of cuttingmaterial thicknesses ranging up to and exceeding two inches. Thinnermaterial may be stacked for cutting multiple pieces simultaneously.

In a typical fluid jet cutting system, a high-pressure fluid (e.g.,water) flows through a cutting head having a cutting nozzle that directsa cutting jet onto a workpiece. The system may draw an abrasive into thehigh-pressure fluid jet to form an abrasive jet. The cutting nozzle maythen be controllably moved across the workpiece to cut the workpiece asdesired. After the fluid jet, or abrasive-fluid jet, genericallyreferred to throughout as a cutting jet, passes through the workpiece,the energy of the cutting jet is dissipated and the fluid is collectedin a catcher tank for disposal. Waterjet and abrasive-jet cuttingsystems of this type are shown and described, for example, in U.S. Pat.No. 5,643,058 issued to Erichsen et al., and assigned to FlowInternational Corporation of Kent, Wash., which patent is incorporatedherein by reference, in its entirety. The '058 patent corresponds toFlow International's Paser 3 abrasive cutting systems.

FIG. 1 is an isometric view of a waterjet cutting system 100 inaccordance with the prior art. The waterjet cutting system 100 includesa cutting head 120 coupled to a mount assembly 104. The mount assembly104 is controllably driven by a control gantry (not shown in detail)having a drive assembly 108 that controllably positions the cutting head120 throughout an X-Y plane that is substantially parallel to a surface110 of a workpiece 112. Typically, the drive assembly 108 may include apair of ball-screw drives oriented along the X and Y axes, each coupledto an electric drive motor. A Z-axis control mechanism 106 is coupled tothe drive assembly and controls the position of the mount assembly in aZ-axis, substantially perpendicular to the surface 110.

Alternatively, the drive assembly 108 may include a five-axis motionsystem. Two-axis and five-axis control gantries arecommercially-available as the WMC (Waterjet Machining Center) and the AFSeries Waterjet cutting systems from Flow International of Kent, Wash.

The cutting head 120 includes a high-pressure fluid inlet 114 coupled toa high-pressure fluid source 116, such as a high-pressure orultrahigh-pressure pump, by a high-pressure line 118. In thisembodiment, the cutting head 120 includes a mixing tube 122 terminatingin a jet exit port 124, from which a high-pressure stream of fluid,i.e., waterjet 126, is emitted and directed at the workpiece 112.

Although the term “mixing tube” is commonly used to refer to thatportion of an abrasive-jet cutting system in which abrasive is mixedwith a high-pressure fluid jet to form an abrasive cutting jet, in thefollowing discussion, “mixing tube” may be used to refer to the nozzlethrough which a jet is discharged, regardless of whether the system usesan abrasive or non-abrasive cutting jet. In addition, the terms“waterjet” or “cutting jet” will be used to refer to the stream of fluid126, also regardless of whether or not the stream includes abrasive.

A particular challenge in waterjet cutting systems is the provision ofan appropriate support for the workpiece, inasmuch as any surface uponwhich the workpiece is supported will be subjected to the cutting forceof the waterjet 126. A common system includes a grid 128 formed by aplurality of slats 130 positioned across a catcher tank (not shown).Upper edges of the slats 130 lie in a plane that is parallel to the X-Yplane. The workpiece 112 is supported on the grid 128 for cutting. Anotch 134 (see FIG. 5) is cut into each slat 130 as the waterjet 126,penetrating through the workpiece 112, passes across the slat. The depthof the notch 134 will depend upon factors such as the traverse speed ofthe waterjet 126, and the thickness and hardness of the workpiece 112.The depth D of the slats 130, as shown in FIG. 1, is selected totolerate significant exposure to the waterjet 126 as it repeatedlypasses across the slat during successive cutting operations. Eventually,damage to the grid 128 reaches a level that the grid 128 must bereplaced.

In operation, ultrahigh-pressure fluid is directed through an orifice(not shown) positioned in the cutting head to form an ultrahigh-pressurefluid jet 126. As discussed previously, the system may or may notentrain abrasive into the jet. The jet exits the mixing tube 122,whereby it is directed toward the workpiece 112. The cutting jet 126pierces the workpiece 112 and performs the desired cutting. Using thecontrol gantry, the cutting head 120 is traversed across the workpiece112 in the desired direction or pattern.

To maximize the efficiency and quality of the cut, a standoff distance S(see FIG. 5) between the jet exit port 124 of the mixing tube 122 andthe surface 110 of the workpiece 112 is controlled. If the standoffdistance S is too small, the mixing tube 122 can plug during piercing,causing system shutdown and possibly a damaged workpiece 112. If thedistance is too great, the quality and accuracy of the cut suffers.FIGS. 2 and 3 illustrate two known devices for determining the positionof the workpiece relative to the mixing tube 122, for the purpose ofestablishing standoff D. The devices described with reference to FIGS. 2and 3 are described in more detail in U.S. Patent Publication No.2003/0037650 in the name of Knaupp et al. and assigned to FlowInternational Corporation of Kent, Wash., which publication isincorporated herein by reference, in its entirety.

The probe 138 of FIG. 2 is configured to extend, via actuation of apneumatic cylinder, until it touches the surface 110 of the workpiece112. The height of the surface 110 is thereby ascertained, the probe 138is then withdrawn, the mixing tube 122 is positioned appropriately inthe Z-axis, and cutting commences. FIG. 2 also shows a shield 136,configured to capture a significant amount of spray-back that occursduring a piercing operation, as described in more detail below.

The contact ring 140 of FIG. 3 is positioned coaxially with the mixingtube 122 and coupled to an actuator via a cantilevered rod 144. Thecontact ring 140 is configured to descend along the axis of the mixingtube 122 until it contacts the surface 110 of the workpiece 112. Theheight of the surface 110 having been established, the contact ring 140may then be withdrawn or may be configured to remain in contact or nearcontact with the surface 110 during the cutting operation. Because asensor associated with the contact ring 140 is capable of continuouslymonitoring the height of the surface 110, the associated cutting systemcan correct for changes in height of the workpiece 112. However, adevice such as the shield 136 of FIG. 2 cannot be used concurrently withthe contact ring 140.

When the system 100 is properly configured, and it cuts a continuousline through a workpiece 112, virtually all of the cutting fluid passesthrough the workpiece 112 to be captured in the catcher tank below.However, at the beginning of a cut while the waterjet 126 is impingingon a surface, but has not yet penetrated the surface, spray-back occurs,in which some or all of the fluid rebounds upward. Primary spray-backoccurs while the waterjet 126 is first piercing the workpiece 112. Inparticular, a large portion of the primary spray-back occurs along anangle reciprocal to the angle of the waterjet 126, and thus, returnsdirectly upward to the cutting device. This high-angle component of thespray-back also retains a significant fraction of the initial energy.Accordingly, it can be very damaging to components of the cuttingsystem, especially in systems employing abrasives in the fluid stream.

FIG. 2 illustrates a spray-back shield 136 according to known art(described in more detail in the '650 publication). The shield 136 isconfigured to block and dampen the high-angle portion of spray-back andsubstantially prevents damage to components of the cutting system by thespray-back, and potential damage or injury to objects in the path of thespray-back.

As previously described, spray-back occurs when the waterjet 126impinges but does not fully penetrate a surface. FIG. 4 illustrates awaterjet 126 traveling in direction T and cutting through a workpiece,and into slats 130 of the grid 128. The waterjet 126 loses energy as itpasses through the workpiece, and cuts a notch 134 into the slats 130 toa depth N at which the energy of the waterjet 126 is insufficient to cutany deeper, although the energy remaining in the stream is stillsubstantial. It may be seen that the advancing front 133 of the notch134 has a curved shape as the waterjet 126 traverses the notch, whilethe bottom of each notch 134 is substantially horizontal.

For the purpose of this description, primary spray-back is thatresulting from reflectance of the waterjet by a workpiece, whilesecondary spray-back results from reflectance of the waterjet by astructure beneath the workpiece.

Unlike the primary spray-back of a piercing operation, secondaryspray-back, as illustrated in FIG. 4, is reflected back by the curvedfront 133 of the notch 134 in a fan shaped spray, in a directionsubstantially opposite the direction of travel T. The spray-back shield136 captures only the highest-angle portion of the secondary spray-back.In some cases, depending on factors such as the speed, direction oftravel T, the condition of the slat 130, the angle of the cut withrespect to the slat 130, etc., a portion of the secondary spray-back canblast back through the kerf 132 of the workpiece 112 at a low angle andtravel some distance from the cutting site. This kind of spray-back willbe attenuated if the system is cutting a curved line, since the curvedwall of the kerf will block some or all of the spray-back.

The most powerful secondary spray-back occurs when the direction oftravel T is incident to the slat 130, that is, when the direction oftravel T is parallel to the slat 130, and directly above, such that thewaterjet 126 passes through the workpiece 112 and impinges directly onthe upper surface of the slat 130 for an extended distance. In thisconfiguration, very little of the cutting fluid can escape downward intothe catcher tank, and so is driven upward through the kerf 132.

The mixing tube 122 is typically fabricated of specially formulatedcarbides to resist wear. Particularly for abrasive cutting systems, themixing tube 122 suffers extreme wear due to its constant contact withhigh velocity abrasives. Thus, mixing tubes are a relatively expensivecomponent of the system. The specially formulated carbides may also bebrittle, and can easily break if the mixing tube 122 collides with anobstruction during operation of the cutting system 100, such asfixturing or cut-out portions of the workpiece 112 which may have beenkicked up during the cutting operation. Accidental breakage of themixing tube 122 increases operational costs and downtime of the cuttingsystem 100.

Several collision sensor systems are known in the art. For example, aring sensor, similar in appearance to the annular sensor 140 of FIG. 3,may be positioned in contact with, or just above the surface of aworkpiece during a cutting operation. An obstruction will make contactwith the ring portion of the sensor prior to contacting the mixing tube122. The sensor is configured to respond to contact with the obstructionby initiating a shut down of at least the drive motors of the cuttingsystem, and generally the waterjet 126 as well, to prevent damage to themixing tube 122, and minimize damage to the workpiece.

Another collision detection system comprises a device having a portionof the cutting head configured to break away without damage to themixing tube, in the event of a collision. The system is described indetail in U.S. Pat. No. 6,540,586, issued to Felice Sciulli et al., andassigned to Flow International Corporation of Kent, Wash., which patentis incorporated herein by reference, in its entirety.

Manipulating a jet in five axes may be useful for a variety of reasons,including, for example, cutting a three-dimensional shape. Suchmanipulation may also be desired to correct for cutting characteristicsof the jet or for the characteristics of the cutting result. Moreparticularly, as understood by one of ordinary skill in the art, a cutproduced by a jet, such as the abrasive waterjet 126 of FIGS. 1-4, hascharacteristics that differ from cuts produced by more traditionalmachining processes.

Two of the cut characteristics that may result from use of ahigh-pressure fluid jet are referred to as “taper” and “trailback.” FIG.5 shows an exemplary illustration of taper. The mixing tube 122 of FIG.5 is traveling along an X-axis, perpendicular to the plane of thedrawing. Taper refers to the angle A of a plane of one wall of the kerf132 relative to a vertical plane. Taper typically results in a workpiece112 that has different dimensions on the top surface 110 (where the jet126 enters the workpiece) and the bottom surface 111 (where the jet 126exits the workpiece).

FIG. 6 shows an example of trailback. The mixing tube 122 of FIG. 6 istraveling in direction T along the X-axis, parallel to the plane of thedrawing. Trailback, also referred to as drag, is a condition in whichthe high-pressure fluid jet 126 exits the bottom surface 111 of theworkpiece 112 at a point behind the point of entry of the jet 126 on thetop surface 110 of the workpiece 112, relative to the direction oftravel T. The trailback angle is the angle B of a line extending througha point of entry to a point of exit of the jet 126 relative to avertical line.

These two cut characteristics, namely taper and trailback, may or maynot be acceptable, given the desired end product. Taper and trailbackvary, depending upon the thickness and hardness of the workpiece 112 andthe speed of the cut. Thus, one known way to control excessive taperand/or trailback is to slow down the cutting speed of the system.Alternatively, in situations where it is desirable to minimize oreliminate taper and trailback while operating at higher cutting speeds,five-axis systems may be used to apply taper and lead angle correctionsto the jet 126 as it moves along the cutting path, as illustrated inFIGS. 7 and 8.

It will be assumed, for the purpose of this description, that theportion of the workpiece to the right of the mixing tube 122 of FIG. 7comprises the finished product, while the portion to the left is scrap.The mixing tube 122 is rotated around an axis parallel to the X-axis,until the right wall of the kerf 132 is substantially vertical.

As shown in FIG. 8, the mixing tube 122 is rotated around an axisparallel to the Y-axis, such that the waterjet 126 is angled into thedirection of travel T until the trailback is substantially eliminated,as shown.

It will be recognized that, as the direction of travel T changes duringthe course of a cutting operation, the fourth and fifth axis rotationscompensating for taper and trailback must change accordingly. A methodand system for automated control of waterjet orientation parameters isdescribed in U.S. Pat. No. 6,766,216 issued to Erichsen et al., andassigned to Flow International Corporation of Kent, Wash., which patentis incorporated herein by reference, in its entirety.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment of the invention, a contour follower deviceis provided, for use with a tool configured to travel along first,second, and third axes. The tool may be part of a waterjet cuttingsystem or other system in which determination of position, distance orangle of a working surface may be advantageous. In the case of awaterjet cutting system having a cylindrical member with an exitaperture, the device includes a plurality of sensor legs having firstand second ends, the first ends coupled to the tool at respective legpositions evenly spaced around the cylindrical member in a first planeperpendicular to an axis of the cylindrical member, each of the sensorlegs being configured to change in length in response to variations ofdisplacement of the respective second ends, the second ends of theplurality of sensor legs together defining a second plane. The devicealso includes a plurality of sensors, each positioned adjacent to arespective one of the plurality of sensor legs and configured to sense alength of the respective sensor leg.

According to an embodiment of the invention, each of the plurality ofsensor legs comprises a cylinder coupled to the device at the respectiveleg position and a sensor shaft having a selected length and first andsecond shaft ends, the first shaft end being positioned in therespective cylinder, the second shaft end extending therefrom, each ofthe plurality of sensor shafts being configured to move axially withinthe respective cylinder in response to variations of displacement of thesecond end of the respective sensor leg. The first end of the sensorshaft of each of the plurality of sensor legs comprises a magnet andeach of the plurality of sensors comprises a hall-effect sensorconfigured to interact with the respective magnet. A bellows,substantially enclosing the respective cylinder and sensor shaft, isprovided for each of the sensor legs. Each of the respective bellows isconfigured to permit travel of the sensor shaft within the cylinder. Ahermetic seal between the respective sensor leg and the device isprovided, and the device further comprises a gas channel configured topermit passage of gas to and from each of the plurality of sensor legsas each of the respective sensor legs expands or contracts.

Processing means is provided for processing a signal provided by atleast one of the plurality of sensors and establishing a distance fromthe second plane to the exit aperture of the cylindrical member, alongthe axis of the member. The processing means may also include means forcontrolling movement of the tool in the third axis, and may furtherinclude means for establishing an angle of the second plane relative tothe first plane, and controlling movement of the tool around fourth andfifth axes lying in a plane parallel to the first and second axes.

According to an embodiment of the invention, a plate is provided,coupled to the second end of each of the plurality of sensor legs, anaperture traversing the plate from a first side to a second side in alocation corresponding to a position of the exit aperture of thecylindrical member. The plate is configured to block secondaryspray-back of the waterjet cutting system.

According to an embodiment of the invention, a collision detectionsensor is coupled to the device and configured to provide a signal inthe event the tool approaches to within a selected distance of anobstruction along the first and second axes. The collision detectionsensor may include a plurality of trigger legs arranged in a circle, thecircle lying in a plane parallel to the second plane, each of thetrigger legs configured to activate the signal when moved inward towardthe tool.

According to an embodiment of the invention, a brush foot is provided,coupled to the second end of each of the plurality of sensor legs, andhaving a substantially circular support ring and a plurality of bristlescoupled to, and extending from, the support ring with outer ends of eachof the plurality of bristles collectively defining a third planeparallel to the second plane. The brush foot is configured to contact awork surface with the outer ends of at least some of the plurality ofbristles, such that a change in angle of the work surface relative tothe first plane is transmitted, via the brush foot, to the plurality ofsensor legs and reflected in a corresponding change in length of eachplurality of sensor legs.

According to another embodiment of the invention, a method of operationis provided.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale.

FIG. 1 is an isometric view of a waterjet cutting system provided inaccordance with prior art.

FIGS. 2 and 3 illustrate details of two known waterjet cutting systems.

FIG. 4 illustrates a waterjet cutting through a workpiece, according toknown art.

FIGS. 5 and 6 show typical cutting characteristics of waterjet cuttingsystems.

FIGS. 7 and 8 show methods of compensation for characteristics picturedin FIGS. 5 and 6.

FIG. 9 is an orthographic view of a contour follower assembly accordingto an embodiment of the invention.

FIG. 10 is a partially exploded view of the contour follower of FIG. 9.

FIG. 11 is a plan view of the contour follower of FIG. 9.

FIG. 12 is a cross-section of the contour follower of FIG. 9, takenalong lines 12-12 of FIG. 11.

FIG. 13 is a cross-section of the contour follower of FIG. 9, shownpositioned on an angled workpiece.

FIG. 14 shows an enlarged view of a small portion of the contourfollower of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

While many of the challenges associated with waterjet machining havebeen described in the background section, there is at least one issuethat has not yet been addressed. It has previously been assumed, for thepurpose of determining the appropriate position of the mixing tube 122,that the upper surface 110 of the workpiece 112 will be substantiallyhorizontal, or will lie in a plane that is parallel to the X-Y plane.Most sensors configured to determine the position of the upper surface110 make that determination prior to the beginning of a cuttingoperation, such as the sensor described with reference to FIG. 2. Evenin the case of the sensor described with reference to FIG. 3, which canbe configured to continually track the surface 110 of the workpiece 112as the cutting operation progresses, such a sensor can only detectchanges in height of the upper surface 110, and cannot determine theangle of that surface, with respect to the X-Y plane.

Accordingly, errors in cutting angle, that is, the angle at which thewaterjet 126 impinges the surface 110, may be introduced into thecutting process because the system is incapable of compensating forvariations in surface angle of the workpiece. Some materials that arecommonly machined using waterjet processes may be less than perfectlyplanar. For example, large pieces of sheet metal may have significantchanges in elevation and contour over the width and breadth of thepiece. Additionally, as a cutting operation progresses, the surface mayshift and flex. For example, the balance of internal stresses that areinherent in the crystalline structure of a steel member may suddenlychange, causing a portion of a large piece of sheet metal to suddenlyflex, altering the relative height and angle of the upper surfacethereof. Systems that do not continually monitor the height of the uppersurface are subject to a collision of the mixing tube against a suddenlyraised portion of the surface, while even systems that do monitor such aheight, cannot compensate for the change in surface angle, relative tothe cutting angle.

Various features and embodiments of the invention will be described now,with reference to FIGS. 9-14.

FIG. 9 is an orthographic view of a contour follower assembly 150according to an embodiment of the invention. The contour follower 150comprises a plurality of subassemblies, including a nozzle nut assembly152, a printed circuit board (PCB) assembly 154, a plurality of sensorleg assemblies 156, a foot plate assembly 158, and a collision sensorassembly 160. The embodiment described herein includes three sensorlegs, though the invention is not limited to that number.

FIG. 10 is a partially exploded view of the contour follower 150,providing additional detail, with respect to the various assemblies, andtheir respective positions. FIG. 11 is a plan view of the contourfollower 150, showing relative positions of many of the components,including the sensor leg assemblies 156, in hidden lines. Details of thenozzle nut assembly 152 that would normally be visible in plan view havebeen omitted to permit a clearer viewing of features of a carbide sleeve224, shown in hidden lines.

Referring now to FIG. 12, a cross-section of the contour follower 150 isshown, taken along lines 12-12 of FIG. 11. As shown in FIG. 12, thecutting head 120 is provided with a collet 121 coupled coaxially to themixing tube 122. The nozzle nut assembly 152 includes a nozzle nut 222configured to engage the collet 121, thereby coupling the contourfollower 150 with the cutting head 120 and the mixing tube 122. Thenozzle nut assembly 152 further includes a carbide sleeve 224 and aresilient sleeve 226. O-ring 168 provides for an interference fitbetween the carbide sleeve 224 and the nozzle nut 222, and is sufficientto hold the carbide sleeve securely during operation. The nozzle nut 222is further provided with barbs 223 configured to receive the resilientsleeve 226 thereon. The resilient sleeve 226 may be formed of natural orsynthetic rubber, or other similar resiliently yielding material.

As previously described, high-angle primary spray-back occurs with greatforce while the waterjet is first piercing the workpiece. The carbidesleeve 224 serves to capture and dampen this spray-back. Fluid reliefapertures 228 vent a portion of the fluid through the wall of thecarbide sleeve 224. The plan view of FIG. 11 shows the carbide sleeve224 and the fluid relief apertures 228 in hidden lines. It may be seenthat the fluid relief apertures 228 are oriented so that abrasive fluidexiting through the apertures 228 is directed between the sensor legassemblies 156, preventing possible damage thereto.

Resilient sleeve 226 provides final damping to fluid exiting the fluidrelief apertures 228. The resilient sleeve 226 is loosely fitted aroundthe carbide sleeve 224, such that passage of the fluid is not impeded,but energy is dampened. Some components of the contour follower 150 aredescribed as being formed of a particular material. Such descriptionsare for illustration only. For example, the carbide sleeve 224 may beformed of any material capable of withstanding the erosive effects ofthe spray-back, including other high-hardness metals, resilientmaterials, or even plastics. Similarly, other references to particularmaterials in describing an embodiment of the invention should not beconsidered limiting, with respect to the scope of the invention.

The PCB assembly 154 comprises a resin or polymer encased printedcircuit board (PCB) 170. In one embodiment, PCB 170 includes a pluralityof hall-effect sensors 172, each positioned directly above one of theplurality of sensor legs 156, as shown in FIG. 11. The hall-effectsensors together define an upper machine plane U that lies perpendicularto an axis of the mixing tube 122.

The resin or polymer encasement of the PCB 170 renders the PCBimpervious to contamination by various materials and substances,especially waterjet cutting fluid and abrasives, such as are ubiquitousduring normal cutting operations. Power and control are supplied to thePCB 170 via cable 173, whose extreme end is also encapsulated with thePCB 170. A grounding strap 188 grounds the PCB 170 to a housing plate174. PCB 170 is mounted on the housing plate 174, which is in turncoupled to the nozzle nut 222, and thereby maintained in a plane thatlies substantially perpendicular to an axis of the mixing tube 122. Aclamp ring 176 engages a perimeter of the PCB 170. Fasteners 177,passing through apertures in the clamp ring 176 and the PCB 170, engagethreaded apertures in the housing plate 174 to retain the clamp ring 176and the PCB 170. The shapes of the PCB 170 and the housing plate 174cooperate with each other so as to fit snugly together. An annularchannel 178 is defined by a narrow gap between the PCB 170 and thehousing plate 174. O-rings 171, positioned in annular grooves formed inthe housing plate 174, seal the annular air channel 178, preventing theentry of fluid or other contaminants.

The housing plate 174 includes a plurality of sensor apertures 184 and avent aperture 186, each in fluid communication with the annular channel178. An elbow fitting 180 is coupled to the vent aperture 186 and a venttube 182 is coupled to the elbow fitting 180 as shown. The vent tube 182has a length sufficient, that a second end thereof is positioned wellaway from the contour follower 150 and the mixing tube 122, and thus isnot susceptible to the entry of contaminants such as cutting fluids andabrasives. Accordingly, air is free to enter the air channel 178 via theelbow fitting 180 and the vent tube 182 without admitting contaminantstherethrough.

Due to the density of detail in FIG. 12, some of the features of thecontour follower 150, and in particular, of the sensor leg assemblies156, are not referenced in FIG. 12, but may be seen more clearly inFIGS. 10 and 13.

Each of the plurality of sensor leg assemblies 156 comprises an uppermember 190 and a lower member 196. The upper member 190 includes anaperture 191 formed coaxially therethrough, and configured to receive asensor shaft 192. The upper member 190 further comprises a mountingflange 193 configured to engage a mounting socket 189 formed in a lowersurface of the housing plate 174, in a snap fit. An upper portion of theaperture 191 corresponds in position to a respective one of theplurality of sensor apertures 184 of the housing plate 174. The uppermember 190 also includes a barbed region 195 configured to receive acylindrical bellows 202 for coupling thereto.

The sensor shaft 192 is positioned within the aperture 191 of the uppermember 190, such that it is free to move vertically within the uppermember 190. The sensor shaft 192 includes a magnet 194 received into anaperture formed at one end thereof. Vertical movement of the sensorshaft 192 causes the magnet 194 to move closer to, or further away from,the corresponding hall-effect sensor 172. A spring 198 is constrainedbetween a lower portion of the upper member 190 at one end and a keeperring 200 coupled to the sensor shaft 192 at the other end, such that thesensor shaft 192 is biased in a downward direction relative to the uppermember 190. Lower ends 185 of the sensor shafts 192 of each of thesensor leg assemblies 156 together define a lower machine plane L.

The lower member 196 includes a bearing surface 197 upon which the lowerend 185 of the sensor shaft 192 is configured to bear. The bearingsurface 197 has a surface area sufficient to accommodate some lateralmovement of the lower end 185 of the sensor shaft 192. The lower member196 further includes a mounting flange 199 configured to be receivedinto a mounting socket 201 of a foot plate 218 via a snap fit. The lowermember 196 further includes a barbed region 203 configured to receivethe cylindrical bellows 202 for coupling thereto.

The cylindrical bellows 202 (see FIG. 12) is coupled at a first end tothe upper member 190 at the barbed region 195 thereof, and to the lowermember 196 at the barbed region 203 thereof. Hose clamps 204, or thelike, serve to secure the bellows 202 in place. Each of the cylindricalbellows 202 is formed of a resilient material and is configured toaccommodate expansion or contraction of the sensor leg assembly 156, asthe sensor shaft 192 moves up and down within the aperture 191. Thebellows is also configured to prevent fluids and other contaminants frominterfering with the function of the sensor leg assembly 156.

As may be seen in FIG. 12, the aperture 191 of the upper member 190 isaligned with, and in fluid communication with, the sensor aperture 184.Accordingly, as the bellows 202 expands and contracts, air within thebellows 202 is free to pass through the air channel 178 and the venttube 182. A passage (not shown) may be provided in the sensor shaft 192or the upper member 190 to facilitate movement of air past the sensorshaft 192 and magnet 194 in the aperture 191. Alternatively, the shapeof the upper portion of the sensor shaft 192 and magnet 194 may beselected to permit passage of air.

The foot plate assembly 158 includes a foot plate 218, a shield plate220, and a foot brush 230. The foot plate has an annular shape andincludes a plurality of mounting sockets 201, each corresponding inposition to one of the plurality of sensor legs 156, and a centralopening. Each mounting socket 201 is configured to receive the mountingflange 199 of the lower member 196 of the respective sensor leg 156 in asnap fit.

The shield plate 220 is formed of an abrasive resistant material, suchas carbide, for example. The shield plate has an annular shape, with araised flange 236 at an inner edge thereof. The raised flange 236 isconfigured to engage the central opening of the annular shaped footplate 218 in an interference fit. Additionally, a retaining ring 234 maybe pressed onto the flange 236 of the shield plate 220 to further securethe shield plate 220 to the foot plate 218.

As has been described with reference to FIG. 4, secondary spray-backresulting from passage of the waterjet 126 over a slat 130 can reflectin a fan shaped spray backward from the direction of travel. For severalreasons, the energy of the spray-back diminishes in direct relation tothe angle of reflectance. Thus, the highest-energy spray-back is thehigh-angle spray captured by the carbide sleeve 224. The shield plate220 has a diameter sufficient to block most of the remaining spray-backthat rises above the surface 110 of the workpiece 112, with a small,relatively low energy, portion being blocked by the foot brush 230. Theflange 236 of the shield plate 220 deflects any spray passing betweenthe carbide sleeve 224 and the shield plate 220.

Most of the primary and secondary spray-back is deflected by variouscomponents of the contour follower 150, as described above. One benefitof this is that the area immediately surrounding a cutting system soequipped is less prone to water spills and damage, and easier to keepdry.

Because a high percentage of cutting operations involves linear cutsalong the X-axis or the Y-axis, and because the most powerful secondaryspray-back occurs in cuts that are in a direction of travel incident tothe slats 130, which are also generally aligned with the X an Y axes,the bottom of the shield plate 220 may wear excessively on linescorresponding to the X and Y axes. Accordingly, the shield plate may beoriented on the foot plate at any angle, and may be rotated periodicallyto evenly distribute the wear.

The foot brush 230 has an annular shape with an inner groove 231 formedaround an inner wall thereof, and an outer groove 237. The groove 231 isconfigured to engage an outer rim 233 of the foot plate 218. The annularshaped foot brush 230 has a radial split 235, which allows the brush 230to be expanded sufficiently to be positioned with the groove 231 inengagement with the rim 233 of the foot plate 218. The foot brush 230further includes a plurality of short bristles 232 extending downwardtherefrom. During operation, the lower ends of the bristles 232 rest onthe upper surface 110 of the workpiece 112, and so conform to a planethereof. This plane may be referred to as the working plane, or workingsurface. It will be recognized that, during cutting operations, thelower machine plane L is parallel to the upper surface 110.

The collision sensor assembly 160 comprises a pressure switch supportring 210 having an annular shape and a ridge 211 formed around an innersurface thereof and configured to engage the outer groove 237 of thefoot brush 230. The support ring 210 is configured to receive a pressureswitch 208 therein. The pressure switch 208 is received in a channel ofthe support ring 210 formed around its circumference, and includes apressure spine 209. The pressure switch 208 is configured such thatpressure against the pressure spine 209 at any point around itscircumference closes a switch. A control cable 216 is configured toelectrically couple the pressure switch with collision sensor circuitry(not shown) for detecting closure of the switch.

A trigger skirt 206 is positioned over the support ring 210, locking thecomponents of the collision sensor assembly 160 together, and securingthe collision sensor assembly 160, together with the foot brush 230,onto the foot plate 218. The trigger skirt 206 may be configured to snapin place. The trigger skirt 206 comprises a plurality of skirt legs 212distributed around its perimeter, and formed integral therewith. Theskirt legs 212 are configured such that pressure against an outer faceof one of the legs 212 will cause the respective leg to flex inward,applying pressure on the pressure spine 209, and thereby closing thesensor switch. Each of the trigger legs 212 includes a lower face 214displaced outward, radially, from an upper portion of the leg. Thisconfiguration permits the leg 212 to flex inward in response to contactwith a sheer vertical surface.

The contour follower assembly 150 comprises an upper section 240,including the nozzle nut assembly 152 and the PCB assembly 154, and alower section 250, including the foot plate assembly 158 and thecollision sensor assembly 160 (see FIG. 10). The upper section 240 isrigidly coupled to the collet 121 of the cutting head 120 by the nozzlenut 222. The lower section 250 is movably coupled to the upper section240 by the plurality of sensor legs 156, each having an upper member 190engaging a respective mounting socket 189 of the housing plate 174, andhaving a lower member 196 engaging a mounting socket 201 of the footplate 218. The lower section 250 of the contour follower 150 is biasedin a downward direction by the springs 198 of each of the sensor legassemblies 156.

In operation, a workpiece 112 is positioned on the support grid 128 of awaterjet cutting system. The cutting head 120, with the contour followerassembly 150 coupled thereto, is lowered until the bristles 232 of thefoot brush 230 make contact with the upper surface 110 of the workpiece112. As the cutting head 120 continues to descend, the bearing surface197 of each of the lower members 196 presses upward against therespective sensor shafts 192, moving the shafts 192 upward within therespective apertures 191, thereby compressing the springs 198. As thesensor shafts 192 rise within the apertures 191, the magnets 194 movecloser to the hall-effect sensors 172. Electrical characteristics of thehall-effect sensors 172 change according to the distance of therespective magnet 194 therefrom, in a manner known in the art. The PCB170 provides a signal via the cable 173 to a position detection circuit(not shown) indicating the position of each of the magnets 194, relativeto the respective hall-effect sensor 172.

According to the embodiment described, the following values are fixedand known: the lower machine plane L, defined by the lower ends 185 ofthe sensor shafts 192 is a known distance from the upper surface 110 ofthe workpiece, defined by the bristles 232; the exit port 124 of themixing tube 122 is a known distance, on the Z-axis, from the uppermachine plane U, defined by the hall-effect sensors 172; and the magnet194 of each of the sensor shafts 192 is a known distance from the lowermachine plane, this distance defined by the length of the sensor shafts192. Given these known values, and given the distance between thehall-effect sensors 172 and the respective magnets, which is derivedfrom the sensor signals, the distance of the exit port 124 of the mixingtube 122 to the upper surface of the workpiece 112 can be determinedwith a high degree of accuracy.

The position detection circuit may be configured to provide a variety ofcalculations, based upon the data provided by the PCB. For example,inasmuch as the lower machine plane L lies parallel to the upper surface110, the data from each of the plurality of hall-effect sensors 172 maybe processed to establish the angle of the upper surface 110 of theworkpiece 112 relative to the upper machine plane U. Alternatively, thedata from each of the plurality of hall-effect sensors 172 may beaveraged to determine the distance of the upper surface 110 from theexit port 124. A third alternative calculation may utilize the data froma single one of the sensors 172, in a case where the upper surface 110of the workpiece is known to be substantially planar, to determine thedistance of the upper surface 110 from the exit port 124. Design andmanufacture of a circuit configured to perform these, and othercalculations are within the capabilities of one having ordinary skill inthe art. Accordingly, the position detection circuit will not bediscussed in detail.

As was described previously, one of the challenges that has notheretofore been adequately addressed, with respect to waterjet cuttingsystems, is the case in which a workpiece does not lay flat on the gridof a cutting system. In the case of a large piece of sheet metal, forexample, measuring perhaps many feet on a side, it is not unusual tofind that such a piece is non-planar, having some portions that exhibitsignificant warp.

Referring now to FIG. 13, a contour follower assembly 150 is shownpositioned on a workpiece 112 that is not laying flat on the upper endsof the slats 130 of a support grid. It may be seen that the lowersection 250 of the device conforms to the upper surface 110 of theworkpiece 112, conforming thereby to the upper surface 110 of theworkpiece 112 over which the cutting head, including the cutting head120 and the mixing tube 122 must travel. Given the signals provided bythe hall-effect sensors 172, which are directly related to the positionof the magnets 194 relative to the sensors 172, the angle of the uppersurface 110, relative to the X-Y plane, can also be determined with avery high degree of accuracy.

In the case of a waterjet cutting system having three axes of control,namely, X, Y, and Z, the position of the mixing tube 122 can be adjustedin the Z-axis to place the exit port 124 at an optimum distance S (seeFIG. 5) from the upper surface 110 of the workpiece at the point wherethe waterjet impacts the workpiece, regardless of the angle of theworkpiece 112. This is not possible with conventional sensors, whichmeasure from a single point, some distance from the mixing tube 122.

In the case of a five-axis system including rotation around X and Yaxes, such as that described with reference to FIGS. 6 and 7, the axialangle of the mixing tube 122 can be adjusted to compensate for a changein the L plane, and by extension, the plane of the upper surface 110 ofthe workpiece 112. Additionally, accurate compensation for taper andtrailback can be performed, independent of changes in the upper plane110.

It will be recognized that, in cases such as that described withreference to FIG. 13, for example, the workpiece 112 will be subject tomovement in the Z-axis as the cutting process proceeds. FIG. 13illustrates a case in which a workpiece does not lie flat on the grid128. A segment 113 supporting a raised portion of the workpiece 112 hasbeen cut away, allowing the workpiece 112 to drop. The upper surface 115of the segment 113 now lies at a different plane than the upper surface110 of the workpiece 112. In such a case, not only must the contourfollower 150 readjust to a new angle, but there is also a danger ofcollision, as some cut edges rise above the upper surface 110.

FIG. 14 shows an enlarged view of a small portion of the contourfollower 150 in the collision condition described above with referenceto FIG. 13. As the cutting head, with the contour follower 150 coupledthereto, travels in direction T, a trigger leg 212 contacts a raisedsegment 113 of the workpiece 112. The trigger leg 212 flexes inward at aregion 213 where the leg 212 joins the trigger skirt 206. The leg 212presses against the spine 209 of the pressure switch 208, causing theswitch 208 to close an electrical circuit. Associated collision sensorcircuitry is configured to shut down the drive of the cutting system inresponse to activation of the pressure switch 208, preventing damage tothe system.

The embodiment described with reference to FIGS. 9-14 includes manyparts that are coupled via interference or snap fit. This facilitatesquick and simple disassembly for servicing or replacement of individualcomponents or assemblies, without the need to remove fasteners, etc.However, other embodiments may incorporate threaded fasteners,retainers, threaded engagements, or any other device or method ofconnection, without deviating from the scope of the invention.

The embodiment described employs hall-effect sensors, which cooperatewith magnets coupled to the sensor shafts. An individual having ordinaryskill in the art will recognize that many types of sensors or signalgenerating devices may be used in place of the hall-effect sensors andmagnets. For example, configurations employing strain gauges,potentiometers, optical sensors, accelerometers, or other sensingdevices may be used. Design and manufacture of such alternateembodiments are within the skill of such an individual, and are withinthe scope of the invention.

An examination of the figures, especially FIGS. 12 and 13, will revealseveral “O” rings that were not specifically described. One havingordinary skill in the art will recognize the value of providing seals atvarious points in such a device, and the function of such “O” rings willbe clear to such an individual.

Alternate embodiments of the invention may not include all of thecomponents described, or may incorporate components or assembliesdescribed herein in systems bearing little obvious resemblance to theembodiment pictured. Such alternate embodiments also fall within thescope of the invention. For example, a cutting or drilling systememploying some other cutting method, such as plasma or mechanical saw,for example, might advantageously incorporate some of the principlesdescribed with reference to the present embodiment.

Alternatively, an embodiment of the invention might incorporate a systemin which a tool is required to be oriented with respect to a surface formeasuring or cleaning. For example, an automated waterjet cleaningdevice might be required to be maintained at a precise angle anddistance from a surface to effectively remove debris, coatings, orcorrosion, without damaging the surface. Other applications may alsooccur to one having ordinary skill in the art, in which the featuresdescribed with reference to the disclosed embodiment may beadvantageously incorporated. Such applications also fall within thescope of the invention.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A device for use with a tool configured to travel along first,second, and third axes, the device comprising: a plurality of sensorlegs having first and second ends, the first ends coupled to the deviceat respective leg positions spaced around the tool in a first planeperpendicular to an axis of the tool, each of the sensor legs beingconfigured to change in length in response to variations of displacementapplied to the respective second ends, the second ends of the pluralityof sensor legs together defining a second plane; and a plurality ofsensors, each positioned adjacent to a respective one of the pluralityof sensor legs and configured to sense a length of the respective sensorleg.
 2. The device of claim 1, further comprising processing means forprocessing a signal provided by at least one of the plurality of sensorsand establishing a distance from the second plane to a first end of thetool.
 3. The device of claim 2 wherein the processing means includesmeans for processing a signal provided by each of the plurality ofsensors and establishing a distance from the second plane to the firstend of the tool.
 4. The device of claim 2 wherein the processing meansincludes means for controlling movement of the tool in the third axis.5. The device of claim 1, further comprising processing means forprocessing a signal provided by each of the plurality of sensors andestablishing an angle of the second plane relative to the first plane.6. The device of claim 5 wherein the processing means includes means forrotating the tool around the fourth and fifth axes.
 7. The device ofclaim 1, further comprising a plate coupled to the second end of each ofthe plurality of sensor legs, an aperture traversing the plate from afirst side to a second side in a location corresponding to a position ofa first end of the tool.
 8. The device of claim 7 wherein the plate isformed, at least in part, from an abrasion resistant material.
 9. Thedevice of claim 8 wherein the abrasion resistant material is a carbidematerial.
 10. The device of claim 1, further comprising a collisiondetection sensor coupled to the device and configured to provide asignal in the event the tool approaches to within a selected distance ofan obstruction along one or more of the first and second axes.
 11. Thedevice of claim 10 wherein the collision detection sensor includes aplurality of trigger legs arranged in a circle, the circle lying in aplane parallel to the second plane, each of the trigger legs configuredto activate the signal when moved inward toward the tool.
 12. The deviceof claim 11 wherein each of the plurality of trigger legs is integral toa support ring and is configured to move by flexing along an upperregion where the respective trigger leg joins the support ring.
 13. Thedevice of claim 11 wherein each of the plurality of trigger legsincludes a lower stepped region, such that the respective trigger leg iscapable of moving in response to contacting a surface substantiallyperpendicular with respect to the second plane.
 14. The device of claim1 wherein the number of sensor legs is three.
 15. The device of claim 1wherein each of the plurality of sensor legs comprises a cylindercoupled to the device at the respective leg position and a sensor shafthaving a selected length and first and second shaft ends, the firstshaft end being positioned in the respective cylinder, the second shaftend extending therefrom, each of the plurality of sensor shaftsconfigured to move axially within the respective cylinder in response tovariations of displacement of the second end of the respective sensorleg.
 16. The device of claim 15 wherein the cylinder of each of theplurality of sensor legs has a longitudinal axis orientedperpendicularly to the first plane.
 17. The device of claim 15 whereinthe first end of the sensor shaft of each of the plurality of sensorlegs comprises a magnet and wherein each of the plurality of sensorscomprises a hall-effect sensor configured to interact with therespective magnet.
 18. The device of claim 15 wherein each of theplurality of sensor legs comprises a respective bellows substantiallyenclosing the respective cylinder and sensor shaft, the respectivebellows configured to permit travel of the sensor shaft within thecylinder.
 19. The device of claim 15 wherein each of the plurality ofsensor legs is configured to form a hermetic seal between the respectivebellows and the device, and wherein the device further comprises a gaschannel configured to permit passage of gas to and from the respectivebellows.
 20. The device of claim 1 wherein each of the plurality ofsensor legs is configured to be coupled, via a snap fit, to the device.21. The device of claim 1, further comprising a brush foot coupled tothe second end of each of the plurality of sensor legs, the brush foothaving a substantially circular support ring and a plurality of bristlescoupled to, and extending from, the support ring with outer ends of eachof the plurality of bristles collectively defining a third planeparallel to the second plane.
 22. The device of claim 21 wherein thebrush foot is configured to contact a work surface with the outer endsof at least some of the plurality of bristles such that a change inangle of the work surface relative to the first plane is transmitted,via the brush foot, to the plurality of sensor legs and reflected in acorresponding change in length of one or more of the plurality of sensorlegs.
 23. The device of claim 1 wherein the plurality of sensors isencapsulated in a polymeric material to form a sensor module.
 24. Thedevice of claim 1, further comprising a cylindrical shield coupled tothe device and positioned coaxially with the cylindrical member, theshield having a plurality of shield apertures distributed around theshield and positioned such that fluid passing from within the shield toan exterior thereof is directed by the shield apertures away from eachof the plurality of sensor legs.
 25. The device of claim 1 wherein thetool is a mixing tube of a waterjet system.
 26. A system, comprising: atool configured to interact with a work surface; and a contour followerdevice coupled to the tool and configured to detect changes of angle ofthe work surface, with respect to the tool.
 27. The system of claim 26wherein the tool is chosen from among a measuring tool, an observationtool, a diagnostic tool, a drilling tool, and a cutting tool.
 28. Thesystem of claim 26 wherein the contour follower device includes aplurality of sensor legs each configured to sense, at a location of therespective sensor leg, a distance between a first plane, perpendicularto an axis of the tool, and the work surface.
 29. The system of claim 26wherein the contour follower device includes a collision detectionsensor configured to detect collision of the device with an obstruction,as the tool moves across the work surface.
 30. The system of claim 26wherein the tool is a waterjet machine.
 31. The system of claim 30wherein the waterjet machine further comprises a cutting head, a catchertank, and a support grid.
 32. The system of claim 30 wherein thewaterjet machine comprises a mechanism for moving a mixing tube alongfirst and second axes substantially parallel to the work surface, andalong a third axis, substantially perpendicular to the work surface. 33.The system of claim 30 wherein the waterjet machine comprises amechanism for rotating a mixing tube around first and second axesintersecting an axis substantially perpendicular to the work surface.34. A device, comprising: a plurality of sensors lying in a first planeand distributed around a central point; a plurality of memberspositioned adjacent to respective ones of the plurality of sensors andmovable along respective axes perpendicular to the first plane, theplurality of members together defining a second plane, each of theplurality of sensors being configured to provide a signal related to adistance between the sensor and the respective member, along therespective axis; and processing means for processing signals from eachof the plurality of sensors and determining an angle of the second planerelative to the first plane.
 35. The device of claim 34 wherein each ofthe plurality of sensors is a hall-effect sensor, and wherein each ofthe plurality of members includes a magnet.
 36. The device of claim 34,further comprising a tool positioned near the central point andconfigured to interact with a surface lying parallel to the secondplane.
 37. The device of claim 34 wherein the tool is a cutting toolpositioned near the central point.
 38. A collision detection device,comprising: a pressure switch lying in a first plane and having asubstantially annular shape and configured to provide a signal whileinward radial pressure is applied at a perimeter of the pressure switch;and an annular shaped trigger skirt lying in a second plane parallel tothe first plane and coaxially with the pressure switch, the triggerskirt including a plurality of trigger legs extending in a directionsubstantially perpendicular to the first plane, each of the trigger legsconfigured to apply inward radial pressure to the pressure switch inresponse to a collision of the device with an obstacle.
 39. Thecollision detection device of claim 38, further comprising a toolpositioned along a central axis of the pressure switch and configured tointeract with a surface lying parallel to the first plane.
 40. A sensorleg assembly, comprising: an upper member having an axially traversingaperture; a sensor shaft positioned within the aperture and configuredto move axially within the aperture, the sensor shaft having first andsecond ends, the first end having a cavity formed axially with theshaft; a magnet positioned within the cavity; and a lower member havinga bearing surface configured to receive the second end of the sensorshaft.
 41. The sensor leg assembly of claim 40, further comprising acylindrical bellows coupled at a first end to the upper member and at asecond end to the lower member, and substantially enclosing the sensorshaft.
 42. The sensor leg assembly of claim 40 wherein the upper membercomprises a mounting flange configured to be received into a firstmounting socket of a contour follower assembly, and wherein the lowermember comprises a mounting flange configured to be received into asecond mounting socket of the contour follower assembly.
 43. A method,comprising: establishing a distance from each of a plurality of pointsdistributed around a tool in a first plane to a second plane at a pointon a line perpendicular to the first plane and intersecting therespective ones of the first plurality of points, the tool defining afirst axis perpendicular to the first plane; and adjusting a position ofthe tool relative to the second plane in response to the distancesestablished.
 44. The method of claim 43 wherein the adjusting stepincludes moving the tool along the first axis.
 45. The method of claim43 wherein the adjusting step includes rotating the tool around a secondaxis intersecting the first axis.
 46. The method of claim 43 wherein theestablishing step comprises measuring a distance from an upper end ofeach of a plurality of shafts relative to the first plane, lower ends ofeach of the shafts defining the second plane.
 47. The method of claim 43wherein the establishing step comprises processing signals from each ofa plurality of sensors located at respective ones of the first pluralityof points.